bpf: selftests: Add selftests for module kfunc support

This adds selftests that tests the success and failure path for modules
kfuncs (in presence of invalid kfunc calls) for both libbpf and
gen_loader. It also adds a prog_test kfunc_btf_id_list so that we can
add module BTF ID set from bpf_testmod.

This also introduces  a couple of test cases to verifier selftests for
validating whether we get an error or not depending on if invalid kfunc
call remains after elimination of unreachable instructions.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20211002011757.311265-10-memxor@gmail.com

1 files changed, 35 insertions, 11 deletions

diff --git a/tools/testing/selftests/bpf/progs/test_ksyms_module.c b/tools/testing/selftests/bpf/progs/test_ksyms_module.c
index d6a0b3086b90..0650d918c096 100644
--- a/tools/testing/selftests/bpf/progs/test_ksyms_module.c
+++ b/tools/testing/selftests/bpf/progs/test_ksyms_module.c
@@ -2,24 +2,48 @@
 /* Copyright (c) 2021 Facebook */
 
 #include "vmlinux.h"
-
 #include <bpf/bpf_helpers.h>
 
+#define X_0(x)
+#define X_1(x) x X_0(x)
+#define X_2(x) x X_1(x)
+#define X_3(x) x X_2(x)
+#define X_4(x) x X_3(x)
+#define X_5(x) x X_4(x)
+#define X_6(x) x X_5(x)
+#define X_7(x) x X_6(x)
+#define X_8(x) x X_7(x)
+#define X_9(x) x X_8(x)
+#define X_10(x) x X_9(x)
+#define REPEAT_256(Y) X_2(X_10(X_10(Y))) X_5(X_10(Y)) X_6(Y)
+
 extern const int bpf_testmod_ksym_percpu __ksym;
+extern void bpf_testmod_test_mod_kfunc(int i) __ksym;
+extern void bpf_testmod_invalid_mod_kfunc(void) __ksym __weak;
 
-int out_mod_ksym_global = 0;
-bool triggered = false;
+int out_bpf_testmod_ksym = 0;
+const volatile int x = 0;
 
-SEC("raw_tp/sys_enter")
-int handler(const void *ctx)
+SEC("tc")
+int load(struct __sk_buff *skb)
 {
-	int *val;
-	__u32 cpu;
-
-	val = (int *)bpf_this_cpu_ptr(&bpf_testmod_ksym_percpu);
-	out_mod_ksym_global = *val;
-	triggered = true;
+	/* This will be kept by clang, but removed by verifier. Since it is
+	 * marked as __weak, libbpf and gen_loader don't error out if BTF ID
+	 * is not found for it, instead imm and off is set to 0 for it.
+	 */
+	if (x)
+		bpf_testmod_invalid_mod_kfunc();
+	bpf_testmod_test_mod_kfunc(42);
+	out_bpf_testmod_ksym = *(int *)bpf_this_cpu_ptr(&bpf_testmod_ksym_percpu);
+	return 0;
+}
 
+SEC("tc")
+int load_256(struct __sk_buff *skb)
+{
+	/* this will fail if kfunc doesn't reuse its own btf fd index */
+	REPEAT_256(bpf_testmod_test_mod_kfunc(42););
+	bpf_testmod_test_mod_kfunc(42);
 	return 0;
 }